Various engine spaces of outboard engine units have been proposed, such as one that comprises a fixed lower casing and an upper covering detachably attached to the fixed lower casing, and one that comprises a lower casing, including a pair of left (port-side) and right (starboard-side) lower cover members, and an upper covering.
One example of the engine spaces is known from Japanese Patent Laid-Open Publication No. SHO-62-18394. In the disclosed engine space, a lower engine cover, which covers a lower section of the engine, is composed of left and right lower cowls that are joined together with their respective edges abutted against each other along a substantially middle portion of the cover, to thereby constitute a lower half section of the engine space.
FIG. 28 hereof schematically shows an example of a structure for joining together the left and right members, along their front and rear edges, of the lower casing 100 in the conventional engine space. Here, the left and right members 101 and 102 have, at their opposed edges 101a and 102a, joining flanges 103 and 104 extending in parallel outwardly in a front-and-rear direction of the engine space. These flanges 103 and 104 are fastened together by means of a horizontal bolt 105 inserted, in a left-and-right direction of the engine space (i.e., in a direction intersecting abutted surfaces or bearing surfaces of the flanges 103 and 104), through holes 103a and 104a formed in the flanges 103 and 104 and threadedly engaged with a nut 106. Thus, the left and right members 101 and 102 of the lower casing are firmly secured together as a unit to thereby provide the lower casing 100. As an alternative of the lower casing 100, the bolt 105 and nut 106 may be received in an elongated recessed portion of an appropriate shape formed (kind of scooped), across the opposed edges 101a and 102a and threadedly engaged with each other, instead of the above-mentioned flanges being formed.
In the conventional engine space, the left and right members, constituting port-side and starboard-side undercover members of the outboard engine unit, have relatively great widths in portions near both of the front and rear ends thereof. Due to such relatively great widths, concave and convex surfaces (projecting and depressed surfaces, i.e. surface unevenness) of the front and rear joining sections would considerably impair the overall outer appearance of the outboard engine unit. Particularly, in the outboard engine unit, such concave and convex surfaces (surface unevenness) tend to be a great block when a large, smooth, continuous surface, such as a flush or even surface, is desired.
Further, in order to reliably prevent water from entering the engine space through between the abutted surfaces of the port-side and starboard-side undercover members when, for example, a following wave is encountered, it is absolutely desirable that the abutted surfaces of the port-side and starboard-side undercover members be secured to each other with maximum tightness.
Generally, the body of the conventional outboard engine units is formed of an aluminum such that the engine of a relatively great weight is mounted on the stern of the boat with sufficient rigidity. Some of the outboard engine units employ resin-made components with a view to reducing the overall weight and costs of the engine unit. In some of the coverings that form the engine space, not only a detachable upper engine cover that defines an upper half section of the engine space but also a lower engine cover that defines a lower half section of the engine space is sometimes formed of resin. In the case where the upper and lower engine covers are formed of resin, it is desirable that an access opening of the engine space, normally formed between the upper and lower engine covers to permit various operations, such as loading, maintenance, etc. of the engine, be as great as possible. In addition, because resin-made components have less rigidity than aluminum-made components, sufficient rigidity is required of the resin-made lower engine cover for supporting thereon the detachable upper engine cover.
One example of such resin-made covers of outboard engine units is disclosed in Japanese Patent Laid-Open Publication No. HEI-6-234393. The HEI-6-234393 publication discloses a resin-made cover having reinforcing ribs to secure necessary rigidity of the cover, and also discloses a technique for avoiding adverse influences of sink marks that would be cased in the resin-made component due to molding of the ribs.
Generally, a fastening structure using bolts or the like is employed to join together resin-made left and right cover members, in which case high rigidity is required of portions of the cover members to be joined. For example, U.S. Pat. No. 4,348,194 proposes a structure for joining together resin-made left and right lower (under) cover members.
According to the technique disclosed in the No. HEI-6-234393 laid-open publication, it is necessary to empirically acquire, through trial and error, appropriate processing that can effectively prevent undesired sink marks from being produced in the reinforcing ribs requiring a relatively great thickness. Acquiring such appropriate processing requires a significant amount of skill and experience, and therefore commercialization of the resin-made cover would require a great amount of time and labor. Further, where the ribs of the resin-made cover members form partition walls of the engine space in conjunction with other components that are to be joined with the covers, the presence of a joining web (denoted by reference numeral 148 in the publication) would create a particular need to allow for a drafting (pulling) direction of a molding die relative to the molding. In addition, the depth of a channel (denoted by reference numeral 188 in the publication), formed along an edge of the cover member, can not be so great in view of a draft angle of the ribs, Consequently, designing freedom or flexibility tends to be considerably limited.
According to the structure for joining resin-made left and right cover members disclosed in U.S. Pat. No. 4,348,194, the left and right cover members are secured together via a bracket by means of two screws. In this case, the cover members have to have sufficient rigidity to remain securely joined together by the screws.